Hi Victoria; thanks for responding.
I tried restarting and loading a copy of the tracklog. As with the first time, nothing seemed to happen other than the tracklog appears in the list of recent tracklogs. Zooming in on the location where the photos were taken shows no record of my route (i.e., no blue track line). If I try to auto-tag the selected images it says "No matching photos".
You would think that if there was something wrong with the format of the GPX file it would produce an error message.